A new autosomal recessive lethal mutation in the mouse designated cartilage matrix deficiency (cmd) is described. Homozygotes are dwarfed, and have abnormally short trunk, limbs, tail and snout, as well as a protruding tongue and cleft palate. The abdomen is distended because the foreshortened rib cage and spinal column forces the liver ventrad from its normal location. Histological and electron microscopic study reveals a deficiency of cartilage matrix in tracheal cartilage and in all cartilagenous bones examined. The syndrome closely resembles the rare lethal condition achondrogenesis, found in human infants, which is also believed to be due to an autosomal recessive gene.